Mill Grinding Process Research Articles

Stirred media mills of fine and ultrafine grinding for subsequent beneficiation operations

This paper presents a brief review of the designs, characteristics, and operating parameters of Stirred media mills supplied by foreign manufacturers. An analysis of information on Stirred media mills , which are used to improve the efficiency of beneficiation and metallurgical operations, is carried out using available publications. The obtained results indicate the inexpediency of using conventional drum ball mills for flotation separation of ores and concentrates with a fine interpenetration of minerals. The application of conventional mills in extraction of ores and concentrates resistant to cyanidation, where gold is finely disseminated in sulfides, is limited by their high power consumption and the corresponding operating costs. In this work, different types of Stirred media mills are considered, including their vertical and horizontal types. The advantages of Stirred media mills over conventional ball mills, particularly in terms of energy efficiency, are noted. The designs and main characteristics of Stirred media mills , which have received wide application, are presented. According to the data presented in the reviewed publications, the main parameters determining the grinding process in such mills are outlined, including the ratio of bead size to mill feed size, density of grinding medium, density of pulp in the mill, volume loading of beads, stirring speed, etc. The conducted analysis of literature data indicated high efficiency of mills based on agitation of grinding media for fine and ultrafine grinding of ores and concentrates in comparison with conventional ball mills. Given that the volume of ores and concentrates resistant to processing by conventional methods is increasing, the application of Stirred media mills is expected become more widespread, thereby increasing the efficiency of subsequent beneficiation and metallurgical operations.

Parameters for the Grinding Process in Vertical Mills Using Optimization Methods

Vertical roller mills, VRMs, are widely used for grinding raw materials in factories engaged in the extraction and processing of minerals. Any machine used for grinding or crushing consumes around 30 to 40% of the energy of a factory. The loading pressure, table rotation speed, moisture content, outlet temperature and pressure rollers are variables that can be controlled to decrease the specific energy consumption Ecs. This paper poses an optimization problem in order to reduce the energy consumption of a VRM used to produce cement and to find the optimal parameters of the operating variables. Several packages are used to solve the nonlinear programming problem, obtaining very concise results, but the results provided by the Pyomo package are used. Comparing the result of the objective function with the energy consumption of a well-known cement company in Ecuador, it is concluded that the optimized parameters are able to reduce by 25% the energy consumption guaranteeing a minimum production of 2200 tons of cement per day, so the model is correctly validated.

Study of the Grinding Process by Friction of Cereal Grains in Stone Mills

The grinding process via friction at the micro-scale in a mill with stones is considered a variable combination of contacts, with two-body (the asperities of lower millstone in direct contact with the asperities of upper millstone) and three-body (micro-particles of ground seeds trapped between the asperities of lower and upper stones of the mill) contacts. Three elements are described: (1) the mechanical contact of the asperities of the lower and upper millstones to predict pressures on asperities by modeling; (2) tests on a millstone sample covered with grinding particles; and (3) tests on a wafer sample formed by the millstones with the grinding particles between them. This paper highlights the combined effects of the micro-scale friction via individual measurements, using an analytical model to sum these effects and validating the model by performing several experiments. An efficiency grind by friction assumes the grain’s movement and interaction between the seeds and solid surfaces, and is highlighted through theoretical and experimental studies. Topography analysis of the surface of the millstones reveals the model of microscopic frictional force. Endpoint measurements (the traces of the surface topography evolution) enable model verification in the grinding process. Thus, the results obtained in the grinding process in the stone mills via friction have practical utility through research benefits. Therefore, they allow for the improvement of quality, reliability, flexible grinding, quality control of the flours, and uniformity degree (fineness/shredding).

AN ASSESSMENT OF INFLUENCE OF SELECTED CHARACTERISTICS OF FEED ON THE RESULTS OF BALL MILL GRINDING PROCESS COURSE FOR POLISH COPPER ORES

The article concerns issues related to the copper ore ball mill grinding process, operating at different technological parameters. The aim of the study was to investigate the influence of various operating parameters and feed characteristics on selected technological effects (comminution degree, yields of the finest particle size classes, ready for downstream flotation operations). The research program included grinding tests of two lithological types of Polish copper ore (dolomite and sandstone) and their mixtures in the proportions: 70% dolomite +30% sandstone and 30% dolomite +70% sandstone. Material was treated under wet and dry grinding in Bond’s ball mill. Three different grinding time were applied together with three levels of mill’s rotational speed. The feed material with three different particle size compositions was used in the rests. The results show that increases in yields of fine particle size fractions for each sample are dependent on the particle size composition of feed, grinding time and rotational speed of mill. Together with increasing of grinding time, fine particle size fraction contents increase too, especially for the coarse feed without fine particles. In general, higher comminution degrees were obtained for ore mixtures, the most favorable results for a mixture of 30% sandstone +70% dolomite, where S 50 equaled 358 and S 90 = 178. Correlation analysis showed that in fact all technological parameters under investigation were significantly related to the obtained comminution effectiveness.

Study of modes and parameters of mineral raw material grinding process in ball drum mills

The paper presents the results of research on the vibration-acceleration signal of the ball mill drum bearing support depending on its load when grinding mineral raw materials. Investigations of vibration sensor readings, installed on the bearing support of the mill drum, and amplitudes of the vibration-acceleration signal from the volumetric filling of the installation drum have been carried out. The dependences of vibro-acceleration signal amplitudes on the frequency spectrum of Fourier series at different volumetric filling of the mill drum in the interval of loads from 0 t/h to 18 t/h are investigated. In research on the interrelation of a signal of vibro-acceleration and consumed power of an electric drive of a drum depending on the degree of its volume filling, their averaged values are established. According to the values of averaged numerical values of amplitudes of vibro-acceleration signal amplitudes, the graphs of their dependence on the frequency spectrum of Fourier series in the range from 0 to 30000 Hz are obtained, the dependences of the consumed power of the ball mill and the amplitude of the vibro-acceleration signal on the volumetric filling of the drum are established, the algorithm of determining the level of filling of the mill drum is developed, the dependences of the vibro-acceleration signal and consumed power on the level of filling of the ball mill in volumetric units are established. It is established that the filling of the mill drum by the consumed power of the electric drive can be controlled up to 0.7 of the volumetric filling of the mill drum. At the same time, the value of volumetric filling of the mill drum, expressed through the signal of vibration velocity of the bearing support, smoothly grows in the whole range of drum filling from 0.0 to 1.0. In this case the reliability of the received information on vibration acceleration of the mill drum support with deviation from the approximating curve, not exceeding 5–6%. Tracking of the level of filling of the mill drum is provided by the signal of the vibration sensor, which allows to maintain of optimal performance, grinding quality, and power consumption. The obtained results give grounds to use the vibration acceleration signal in the system of automatic control of the coal grinding process as a criterion for evaluating the degree of filling of the mill drum during its operation. Keywords: ball drum mill, grinding, vibration acceleration signal amplitudes, coal.

Automated system for control and monitoring of explosion safety of the coal grinding process in ball drum mills

The article presents the results of research on automated systems of control and monitoring of explosion safety of dust and gas mixture during coal grinding in ball drum mills (BDM). The problem of the gas-dynamic factor, which arises at the disintegration of coals of middle stage of metamorphism (gas coals) in the atmosphere of closed or limited space, for example in mine workings, chambers, furnace furnaces, etc., is considered. Earlier, when burning anthracite coals, such a problem did not arise, since anthracite does not have a gas component of hydrocarbons. Therefore, all automated control systems were developed from the condition of grinding quality and optimal loading of the BDM. The work aims to develop an automated system of control and monitoring of explosion safety of coal-gas mixture in ball drum mills in the process of grinding gas coals in preparation for combustion. It is established that the sizes of coal grinding fractions in the BDMs from 50 microns to 250 microns correspond to the sizes of supermelonites from 10 microns to 200 microns to particles that are formed during sudden coal and gas emissions in mines. Coal supermelonites are the main source of gas emission into the atmosphere of mine workings, as at their formation there is the disintegration of the supramolecular organization of coal macromolecule and generation of methane. Crushing of gas coals in the BDM inevitably leads to the formation of the explosive methane-coal mixture, which further enters the furnace of the boiler unit. As a result, a new functional scheme for automatic regulation and optimization of parameters of the BDM with a measuring and computing system for controlling the temperature of the gas medium, pressure drop, and a self-tuning microprocessor controller was developed. A technological scheme for installing control and measuring equipment has been developed for preparing coal for burning in a thermal power plant boiler unit. Explosion safety control in the technological cycle of preparing gas coals for burning is carried out constantly using methane and oxygen concentration sensors. The operability of the control system was confirmed on the industrial mill of the boiler unit BKZ-160-100PT TPP of "Kramatorskteploenergo" TPP. Keywords: ball drum mill, coal grinding, methane, explosion safety, control system.

Intensifying the cement grinding process

This article deals with the intensification of the grinding process in ball mills. Attention is drawn to the need to reduce the energy input for grinding. Data on cement clinker grinding kinetics when surface-active agents are used, as well as issues of intensification of the grinding process by changing the surface profile of the armor plates are given.

MODEL ADAPTIV NEURO-FUZZY PENTRU SISTEMUL DE CONTROL AL PROCESULUI DE MACINARE A CLINKERULUI IN MORILE CU BILE DIN FABRICILE DE CIMENT

The main purpose of this study consisted in the realization of the development model of a decision support system for the cement grinding process in ball mills, including the acquisition, processing and analysis subsystems of data regarding the progress of the technological process, based on hardware technologies and intelligent software. To create the decision-making models, the graphic environment for the development of adaptive neuro-fuzzy systems from the Matlab program package was used. The paper presents a model based on the techniques proposed and developed with the application of fuzzy logic and artificial neural networks. The input/output variables, the linguistic qualifiers and the membership functions specific to each shredding batch were identified. The inference rules were defined. A standard defuzzification method was applied to defuzzify the results obtained from the inference process. At the same time, the results of the simulations of the proposed models in the Matlab environment were also presented. The testing and verification of the data obtained with the proposed inference model was carried out by comparison with the experimental data.

Prediction of cement specific surface area in the cement mill grinding process: A method combining dual-frequency principal component analysis and extreme gradient boosting

The cement specific surface area is an important indicator of cement quality. The accurate prediction of the cement specific surface area aims to guide operators to control the cement grinding process to improve product quality while reducing system energy consumption. However, due to the complexity of the cement grinding process, the process variables have coupling, time-varying delay, nonlinear characteristics, and different sampling frequency. Herein, we proposed the specific surface area prediction model, which combined dual-frequency principal component analysis and extreme gradient boosting (DF-PCA-XGB). In order to solve the problem of difficulty in modeling due to different sampling intervals of related data, this paper analyzes the low-frequency sampling data and high-frequency sampling data under multiple working conditions, and establishes prediction models respectively. Aiming at the data redundancy problem of high-frequency and low-frequency variable data in the introduced time window, a method based on the combination of principal component analysis (PCA) and extreme gradient boosting (XGB) cross-validation is proposed to reduce data redundancy while retaining most of the characteristics of the data. The final specific surface area prediction results were obtained by weighting the high-frequency data model and the low-frequency data model. The simulation results showed that the prediction method in this paper can improve the prediction accuracy of the specific surface area of the finished cement product under multiple working conditions with high stability and has promising application in the cement manufacturing process.

СОСТОЯНИЕ И НАПРАВЛЕНИЯ РАЗВИТИЯ ТЕХНИКИ И ТЕХНОЛОГИИ ИЗМЕЛЬЧЕНИЯ

The analysis of the state and direction of development of equipment and technology for grinding materials in the Russian and foreign cement industry is carried out. The equipment used for grinding with ball mills, vertical mills and press-roll grinders is considered. The effectiveness of the use of ball mills and their advantage over other grinding units used in large-capacity production is shown. One of the main directions for the development of the efficiency of the grinding process in ball drum mills has been determined. It consists in the development of intra-mill devices that are aimed at destroying stagnant zones in the feed, intensifying the work of grinding bodies and creating conditions within the mill classification of the crushed material. The design and principle of operation of a ball drum mill equipped with an inclined inter-chamber partition is described. It ensures the transverse-longitudinal movement of grinding bodies in the mill body. The advantages of using an inclined inter-chamber partition are given, which include a reduction in the weight of the mill load and the hydraulic resistance of partition, improved aspiration, reduced power consumption and provision of transverse-longitudinal movement.

Improving the efficiency of the coal grinding process in ball drum mills at thermal power plants

Ensuring the reliable operation of the dust fuel preparation system at thermal power plants (TPP) is a topical issue since it determines the energy strategy of any country that fires coals for thermal energy production. This unit is one of the most energy-intensive units in TPP. Those systems are outdated, poorly automated and high energy-intensive. Furthermore, they must ensure efficient and safe operation of the facility while being environmentally friendly. The current work focuses on the process of grinding coals in ball drum mills for further pulverized combustion. An experimental study was performed in order to determine the main factors (rotational speed of the drum mill, the degree of loading with the grinding balls, and the velocity of the supplied air) that affect the efficiency of the fuel preparation system. The obtained experimental data and performed mathematical modeling resulted in regression equations describing the energy performance of the mill. Three regression equations for mill productivity, power consumed, and specific surface area of the final product were obtained and validated. The study reveals that the lowest specific energy consumption is achieved when the relative rotational speed of the mill is between 0.81 and 0.87; the weighted average diameter of the balls ranges from 33.5 up to 34.5 mm; the load factor of the grinding media ranges from 0.325 up to 0.335, the supplied air velocity is between 0.2 and 0.3 m/s. The proposed methodology allows adjustment of the operating parameters of the grinding process to achieve the lowest energy consumption. The power consumption for the preparation can be reduced up to 5 % for the selected operation mode of the grinding facility.

Establishing the conditions for the formation of a near-wall layer of solid granular fill of a rotating drum

This paper reports the assessment of the influence of dynamic motion parameters on the formation and disappearance at the cylindrical surface of the chamber of the rotating drum of the near-wall layer of non-loose granular fill. Based on the results of experimental visualization of the flow, the effect of solidity on the behavior of granular fill was revealed. The hydrodynamic effect of fill quasi-liquefaction under the action of solidity has been established, which involves the occurrence of a connecting interaction between adjacent layers and the surface of the chamber. Conversion of shear circulation flow to homogeneous dense clustered stream with slipping and rolling without relative movement of particles was detected. The hydrodynamic characteristics of circulation flow transition to the near-wall layer mode during rotation acceleration have been defined. Such a transition is implemented by smoothly increasing the thickness of the layer when the rest of the fill is circulated at the bottom of the chamber. The effect of the rheological hysteresis of the movement of the rotating chamber fill, caused by quasi-liquefaction of non-loose granular environment, has been established. The effect implies exceeding the speed limit ωfl in the formation of a near-wall layer, at rotation acceleration, above the boundary ωdl of the layer disappearance when the rotation slows down. The manifestation of hysteresis mainly increases with an increase in Reynolds number. The intensity of increased hysteresis manifestation increases with a decrease in the degree of filling the chamber. The value of the Froud number for the ωfl and ωdl boundaries increases with the increase in Re. It has been established that at the relative particle size of the dispersed fill ψdc≈(0.065–1.04)·10‑3 and Re=30–500, Fr=1–2.9, for the ωfl boundary, and Fr=0.5–1.4, for the ωdl boundary. The Fr value for the ωfl limit was found to exceed this value for the ωdl boundary by 1.6–2.1 times. The established effects make it possible to substantiate the rational parameters for the grinding process in drum-roll mills

Capacity of roller mill for cement grinding

Engineering for the cement industry is part of the heavy industry. The cement industry is the main supplier of raw materials for the production of concrete and reinforced concrete. For grinding cement, two types of mills are used - ball and roller. Recent decades have proven the great effectiveness of a vertical roller mill for grinding raw materials. Its effectiveness, combined with the implementation of drying, grinding and separation in one unit, gives it an undeniable advantage over a ball mill. This explains the significant increase in the share of roller mills in the cement mill market. The grinding process in such mills occurs due to abrasion, respectively, in the process of work wear of the rubbing parts of the mill occurs. The work evaluated the performance of a mill with smooth disk rolls. During the study, the cause of the destruction of the sectors of the mill produced by FLSmidth, operating in the Russian Federation, was identified. The study revealed the causes of the destruction of the details of the roller mill: with the simultaneous impact of the workload and the displacement of the sectors resulting from intensive wear, the total equivalent stresses exceed the value of the endurance limit under cyclic loading. Therefore, the accumulation of fatigue damage to the material, the formation and growth of cracks, which adversely affects the performance of the mill. A number of measures have been proposed to increase the operability of mills of this design.

Predictive Controller Design for a Cement Ball Mill Grinding Process under Larger Heterogeneities in Clinker Using State-Space Models

Chemical process industries are running under severe constraints, and it is essential to maintain the end-product quality under disturbances. Maintaining the product quality in the cement grinding process in the presence of clinker heterogeneity is a challenging task. The model predictive controller (MPC) poses a viable solution to handle the variability. This paper addresses the design of predictive controller for the cement grinding process using the state-space model and the implementation of this industrially prevalent predictive controller in a real-time cement plant simulator. The real-time simulator provides a realistic environment for testing the controllers. Both the designed state-space predictive controller (SSMPC) in this work and the generalised predictive controller (GPC) are tested in an industrially recognized real-time simulator ECS/CEMulator available at FLSmidthPvt. Ltd., Chennai, by introducing a grindability factor from 33 to 27 (the lower the grindability factor, the harder the clinker) to the clinkers. Both the predictive controllers can maintain product quality for the hardest clinkers, whereas the existing controller maintains the product quality only up to the grindability factor of 30.

Neural simulation of ball mill grinding process

This study is aimed at getting simplified model of mill filling technological process of fine crushing in a closed-circuit grinding with screen separation. Optimal and simple model structure are supposed to be used in adaptive predictive control loop. The minor factors that directly affect the mill load indicator are not taken into account, since some of them cannot be directly measured, and other ones affect the process only in the long term. In this paper the athors considered mill filling process identification in the center-discharge ball mill by the method of neural networks (NN). The method includes the identification of the nonlinear process using nonlinear autoregressive with external input (NARX) neural network. The most accurate model was found by varying the structural parameters of the network. The best models were tested in the course of the actual grinding process. The best estimation of the NN model to the real object is obtained with 72.1% match.

STUDYING THE EFFECT OF ORE TEXTURE ON THE BOND WORK INDEX AT THE MAHD AD DAHAB GOLD MINE: A CASE STUDY

The grinding process in industrial ball mills is the basic unit and most energy-consuming component. Therefore, great economic gains will be achieved if a slight improvement occurs in the efficiency of grinding. The variation of gold ore petrography affects its mechanical properties which in turn, affects the grinding process. In this investigation, different gold-bearing ore types from the Mahd Ad Dahab gold mine were tested. As a part of the current study, some of the me- chanical and physical properties including strength properties, geological characterization and Bond work index were determined. This investigation showed that the Bond work index increases with an increase in rock strength properties. The maximum difference in the Bond work index for the five tested gold ores was 11%. Whereas, an average interval between the two-sequence types of the tested ore was approximately 2.5%.

Intensification of the grinding process in vibration mills

The paper deals with the problems of intensification of grinding in vibration mills with harmonic, biharmonic and polyharmonic vibrations. In particular, as one of the ways to solve this problem, it is suggested to use the adjustable amplitude-frequency characteristics of the movement of the vibrator with polyharmonic vibrations. The paper presents a new design of the vibration mill with polyharmonic vibrations, which has three vibratory drives mounted on the grinding chamber with the possibility of varying the frequency, direction of rotation, mass of unbalanced masses, as well as the geometric arrangement of the vibratory drives relating to the axes passing through the center of gravity of the vibration mill.

An attempt to increase technological capabilities of laboratory vibratory mills by changing the construction of chamber

Abstract The paper presents the issues related to the grinding process in the vibration mills with low vibration frequency. These mills are rated among devices with high energy of impacts with much wider potential of industrial use than the classic gravitation mills. In vibratory mills there is an unfavorable decrease in the intensity of the grinding process along with the increase in the chamber diameter, which makes it impossible to achieve high performance of such devices. One of the ways to reduce or eliminate this occurrence is to intensify the load movement inside the chamber – this is the subject of this article. The article shows that in a vibrating mill of periodic action it is possible to increase its technological capabilities by application of an appropriate cylindrical component permanently installed inside the milling chamber. The paper also presents an attempt to increase the technological capabilities of a laboratory continuous vibratory mill.

Development of a Cutting Force Prediction Model for Silica/Phenolic Composite in Mill-grinding

A cutting force model was developed from silica/phenolic composites for mill-grinding process. The experimental was carried out on silica/phenolic material and found that the cutting force decreased significantly with the increase of cutting speed, whereas the same was found increased with the increase of feed rate and cutting depth. By comparison of the experimental and simulation data of the cutting force, it was found that the errors are below than 30 % in most of the sets of parameters. The variation found is due to the heterogeneity and other complex properties of silica/phenolic composites. The results were almost the same as previous experiments. So, the cutting force model developed in this paper is robust and it can be applied to predict the cutting force and optimization of the process.

Impact of chloride grinding aid with modified fly ash using topdown nanotechnology on grinding performance

The influence of Grinding Aid (GA) and Grinding Performance (GP) on Raw Fly Ash (RFA) have been analyzed by solid state route to obtain Chloride based Ground Fly Ash (CGFA). Particle size distributions of RFA and CGFA are studied and GP optimization occurred at 120 min. Crystal structures are examined by X-ray Diffraction (XRD) and found to be multiphasic. Crystallite size and microstrain measured using Williamson-Hall plot (from XRD pattern) reveal that reduction in size and lattice gets strained. Microstructure obtained by Scanning Electron Microscope (SEM) shows <5 μm grain size with a spherical shape. Normal consistency found to be increased for both RFA and CGFA when compared to a control sample, whereas setting time is getting increased for RFA and decreased for CGFA. In addition, optimized compressive strength of RFA (15%) and CGFA (45%) blended cement composite mortar shows the higher strength of 6% and 7% respectively. The ball mill grinding process using chloride based grinding aids can be adopted at high volume replacement of fly ash in cement manufactory.